7d and CF card speeds

hi all - i was undure where to find this info:

i was interested in upgrading my CF card. I have sandisk 16GB extreme cards (up to 45mb/sec)
and I liked the prices of the sandisk extreme 32gb up to 120mb/sec versions now available.

but

can the camera actually utilize any of those speeds to my benefit?
i mean, besides the increase in volume of memory

and where can i read about that?

many thanks

Sandisk recommends their 60MB/s memory cards in your choice of sizes.

http://pct1.sandisk.co​m …d=1002&dtid=7&h​dnSiteID=1

Any faster than 60MB/s is likely to be wasted on the 7D, but might be usable in a future camera model.

Personally I don't like to put all my eggs in one basket, so I use 8GB and 16GB memory cards in my 7Ds and 5DII.

ceriltheblade wrote in post #16903259
can the camera actually utilize any of those speeds to my benefit?

good question, it's not been updated recently but some useful data here: http://www.robgalbrait​h.com …t_col=burst&sor​t_dir=DESC

amfoto1 wrote in post #16903289
Sandisk recommends their 60MB/s memory cards in your choice of sizes.

http://pct1.sandisk.co​m …d=1002&dtid=7&h​dnSiteID=1

Any faster than 60MB/s is likely to be wasted on the 7D, but might be usable in a future camera model.

Personally I don't like to put all my eggs in one basket, so I use 8GB and 16GB memory cards in my 7Ds and 5DII.

thanks for the link. According to it though, in the "suggested cards" area - they included the 120mb/sec versions as well.

joeseph wrote in post #16903308
good question, it's not been updated recently but some useful data here: http://www.robgalbrait​h.com …t_col=burst&sor​t_dir=DESC

this was very useful. I am pretty sure that I have the newest frimware set on the 7d - allowing me the UDMA 7 cards...so that is good. And the difference between cards that he tested on the 7d is quite impressive and not necessarily dependent on price alone. Heck, Sandisk isn't even in the top 5! This is enough to get to me to change the idea completely and go with lexar (i have had previous good experience with them too) 1000X cards.

thanks guys for all the useful info!

In my measurements the time to fill the buffer is the same no matter what the card speed. The time to empty the buffer is dependant on card speed, up to around 50 MB/s - a 60 MB/s card empties the buffer just one second faster than a 45 MB/s card. So a 130 MB/s card would be overkill as far as your camera is concerned.

Please note the correct units for speed - MegaBytes per second, not millibits per second. One is 10 billion times faster than the other.

many thanks Hollis for pointing out my grammatical error : indeed I meant MB/s and not mb/s.

i read your post that you linked above - and the post linked by joseph, and I would be interested in understanding the difference in your results. Methodology doesn't seem dramatically different. Maybe it could be because you used different and older cards? Even on Rob Galbraith's posted results, there was a difference between same cards just with different volumes. I would be interested to hear what you think of the issue. If I remember correctly the date of your post vs the release of the firmware fix which dealt with UDMA7 cards as well, your calculations were pre-release. Correct?

I've not looked at Rob's methodology in detail.

The firmware update should make no difference as Canon specifically state that the extra speed of UDMA7 would not be accessible.

The faster speed of the cards is more designed for video than for stills

digger58 wrote in post #16904683
The faster speed of the cards is more designed for video than for stills

Nope. Video is extremely undemanding when it comes to card speed. According to the 7D manual all you need is a card capable of 8 MB/s for full HD.

hollis_f wrote in post #16905485
Nope. Video is extremely undemanding when it comes to card speed. According to the 7D manual all you need is a card capable of 8 MB/s for full HD.

But it may take a quite fast card to actually manage 8 MB/s unless the card has been pre-erased.

A card that is specified to manage 10 MB/s continuous write speed is a card that is fast enough to manage that write speed even when the flash sectors are dirty and needs to be erased before they may be used. A card that only manages 10 MB/s with all flash sectors pre-erased will not be even close to 10 MB/s when there is old file data to be erased before the sectors can be reused.

It's just that removing files from a card doesn't erase the "surface" of the card unless the camera or PC and the used card supports trim functionality, where the card memory controller gets information that says "block x, y and z are now no longer in use, so it's ok to erase them in preparation for new writes".

So people who pre-clear their cards before shooting video can manage with a slower card. Without the pre-clear, the card must have excess speed, because the video writes will be bursty - wait for erase, then quick write, then wait for erase, then quick write. And the writes must be fast enough to "mask" the time spent erasing flash sectors. This is a reason why we have got "low level format" functionality. An incorrect term just to separate a format where all flash sectors gets erased from a format that just rewrites the file allocation table and root directory.

does pre-clear mean to reformat the card?

ceriltheblade wrote in post #16905510
does pre-clear mean to reformat the card?

Either a full reformat of the card, or erasing the photos with a camera or computer that supports sending trim commands to the card so the card controller gets to know exactly what bytes that was occupied by erased photos and so understands what flash blocks that can be rearranged and erased.

A normal file erase doesn't involve the sectors where an image is stored - it's just a removal of the file name from the directory, and a file allocation table marks the sectors as empty. But the memory controller inside the card doesn't understand anything about file systems, so it can't deduce that these writes to the card represents that other blocks on the card are now free to be erased.

I don't remember what the command is called for SD cards but for SSD and for CF cards, a command 'TRIM' was added, where the OS can specifically report the addresses consumed by a removed file to the memory controller to allow a pre-erase before the OS sometimes later needs to reuse the sectors and issues a write command to these sectors.

thank you for that clarification. I was unaware of that. So do you periodically reformat your cards?

ceriltheblade wrote in post #16905599
thank you for that clarification. I was unaware of that. So do you periodically reformat your cards?

No. But there isn't a requirement to do so. If the card is fast enough, then it can manage to do the erases late, i.e. just when it does need the space.

And if the files are erased by an OS that issues TRIM commands, then the erase will happen automatically.

Don't worry about these things unless you actually see a need for it.

pwm2 wrote in post #16905503
But it may take a quite fast card to actually manage 8 MB/s unless the card has been pre-erased.

Yes, a blisteringly fast 20 MB/s card!!!!

(Can you actually buy a CF that slow nowadays?)